1. Field of the Invention
Alloys for the medium temperature range for heat engines based on intermetallic compounds, which are suitable for directional solidification, are replacing stainless steels and in part supplement the conventional nickel-based superalloys or are replacing other intermetallic compounds.
The invention relates to the further development and improvement of the alloys based on an intermetallic compound of the iron aluminide Fe.sub.3 Al type using further additives which improve the mechanical properties (strength, toughness, ductility).
In the narrower sense, the invention relates to an oxidation- and corrosion-resistant alloy for components for a medium temperature range based on doped iron aluminide Fe.sub.3 Al.
2. Discussion of Background
Intermetallic compounds and alloys derived therefrom have recently been gaining increasing importance as materials which can be used in the medium and high temperature ranges. Nickel aluminides and titanium aluminides, which in part supplement or replace conventional nickel-based superalloys, are generally known.
The various iron aluminides have been known for a long time, in particular as oxidation-resistant and non-scaling protective coats on components made of iron and steel. Because of their relative brittleness, these intermetallic compounds, which are produced by spraying aluminum onto steel bodies and then annealing, have, however, hardly been considered as construction materials. Recently, however, in particular the iron-rich alloys located in the vicinity of the Fe.sub.3 Al phase have been investigated in more detail in respect of their suitability as materials for the temperature range from room temperature up to about 600.degree. C. It has also already been proposed to improve their properties by co-alloying further elements. Materials of this type have been able to compete successfully with the conventional corrosion-resistant steels in the temperature range around about 500.degree. C. With respect to the prior art, the published documents are cited below:
H. Thonye, "Effects of DO.sub.3 transitions on the yield behaviour of Fe-Al Alloys", Metals and ceramics division, Oak Ridge National Laboratory, Oak Ridge, Tenn. 37831, Mat. Res. Soc. Symp. proc. Vol 39, 1985 Materials Research Society. PA1 S. K. Ehlers and M. G. Mandiratta, "Tensile behaviour of polycrystalline Fe-31 at.-% Al Alloy", Systems Research Laboratories Inc., Dayton, Ohio 45440, TMS Annual Meeting Feb. 1982, The Journal of Minerals, Metals and Materials Society. PA1 Al=24-28 at.-% PA1 Nb=0.1-2 at.-% PA1 Cr=0.1-10 at.-% PA1 B=0.1-1 at.-% PA1 Si=0.1-2 at.-% PA1 Fe=remainder
The known alloys based on Fe.sub.3 Al do not yet satisfy the technical requirements in all respects. There is, therefore, a need for their further development.